<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
	</head>
	<body>
	<button class="btn" id="box">按钮</button>
	<div>点我</div>
	<script type="text/javascript">
		document.querySelector(".btn").onclick = function(){
			alert("欢迎光临")
	}	
		
		
		
		
		
		
	</script>
	</body>
</html>
